Many conventional pen input/display devices adopt a tablet-integrated display panel (display panel integrated with a transparent tablet) to enable pen input on the display screen. There are various types of tablet-integrated display panels; the most popular among them are those with a transparent tablet operating in a resistor film scheme. In such a display panel integrated with a transparent tablet operating in a resistor film scheme, the transparent tablet is placed in front of the display panel to sense coordinates.
So, in the tablet-integrated display panel, the transparent tablet is sandwiched between the display panel and an input pen tip in pen input operation. The structure gives rise to a problem of “parallax” where the pen tip exists away from the display position on the display panel. Another problem is that the transparent tablet, although transparent, lowers the surface brightness of the display screen for it is placed on the display panel.
These problems are addressed by ultrasonic pen input scheme which allows pen input with no transparent tablet being placed on the display panel. In the scheme, an ultrasonic transmitter is provided in the input pen and sends ultrasonic sound to a receiver on the display panel. The relative position of the input pen to the display panel is computed from the received information so as to obtain the input position. Specifically, a distance is calculated according to counter scheme where the time which ultrasonic sound from an ultrasonic transmitter takes to reach a receiver is measured in terms of clock counts, and the distance is calculated based on the time measurement and the speed of sound.
The ultrasonic pen input scheme is disclosed in, for example, U.S. Pat. No. 4,814,552 (issued Mar. 21, 1989).
Now, the ultrasonic pen input scheme is described in more detail with reference to FIG. 18 through FIG. 21.
The U.S. patent is shown in FIG. 18(a). A pen input unit 101 is placed near a display panel 100. On the pen input unit 101 are two ultrasonic receivers 102, 103 and an infrared receiver 104. An input pen 120, shown in FIG. 18(b), is equipped with an ultrasonic transmitter 121 and an infrared transmitter 122. The input pen 120 has a pen tip 123 acting as a switch 124.
Moving on to FIG. 19, the input pen 120 contains: ultrasonic transmission circuitry 125 driving the ultrasonic transmitter 121; infrared transmission circuitry 126 driving the infrared transmitter 122; and a microcomputer 127 controlling outputs from the ultrasonic transmitter 121 and the infrared transmitter 122.
Under the control of the microcomputer 127, the ultrasonic transmitter 121 and the infrared transmitter 122 send a signal when the input pen 120 contacts the display panel 100, turning on the switch 124 on the pen tip 123. The ultrasonic transmitter 121, infrared transmitter 122, ultrasonic transmission circuitry 125, infrared transmission circuitry 126, and microcomputer 127 receive operational power from a built-in battery (not shown) inside the input pen 120.
Next, an input position computation method is described in accordance with the ultrasonic pen input scheme.
As the input pen 120 contacts the display panel 100, the built-in switch 124 on the pen tip 123 is turned on. Then, the ultrasonic transmitter 121 and the infrared transmitter 122 simultaneously send an ultrasonic signal and an infrared signal respectively. The ultrasonic receivers 102, 103 individually measure a signal travel time the ultrasonic signal takes to reach a receiver after leaving the transmitter. The infrared signal is regarded as taking no time to reach the infrared receiver 104 after transmission. The reception of the infrared signal triggers the measurement of the signal travel time as shown in FIG. 20.
The signal travel time of the ultrasonic signal is measurable by, for example, counter scheme. Specifically, the times which the ultrasonic signal from the ultrasonic transmitter 121 takes to reach the ultrasonic receivers 102, 103 are measured in terms of clock counts which are then multiplied by the clock cycle to obtain the signal travel times.
The signal travel times calculated in the ultrasonic receivers 102, 103 are multiplied by the propagation speed of the ultrasonic signal, that is, the sonic speed, to obtain the distance by which the ultrasonic transmitter 121 is separated from the ultrasonic receivers 102, 103 at that particular time. The distance between the ultrasonic receivers 102, 103 is known in advance.
Hence, the distance L1 between the ultrasonic transmitter 121 and the ultrasonic receiver 102, the distance L2 between the ultrasonic transmitter 121 and the ultrasonic receiver 103, and the distance L0 between the ultrasonic receiver 102 and the ultrasonic receiver 103 are now all obtained (see FIG. 21). From these three distances, the position of the ultrasonic transmitter 121 is obtained which is expressed by a set of positional coordinates (X, Y) of a point on the display panel 100. The coordinate position of the ultrasonic transmitter 121 detected in this manner is used as the pen tip coordinate position.
Next, the input position computing operation, i.e., the detected coordinate position, will be described in more detail with reference to FIG. 22 and FIG. 23.
Referring first to FIG. 22, an ultrasonic signal from the ultrasonic transmitter 121 in the input pen 120 is received by the ultrasonic receivers 102, 103 in the pen input unit 101. The incoming waveform is amplified in amplifier circuits 105, 106 and converted from analog to digital in A/D converter circuits 107, 108, before being transferred to a travel time difference count circuit 109.
Meanwhile, an infrared signal sent out from the infrared transmitter 122 simultaneously with the ultrasonic signal is received by the infrared receiver 104 in the pen input unit 101 and amplified in an amplifier circuit 110, before being transferred to the travel time difference count circuit 109 similarly to the ultrasonic signal.
The travel time difference count circuit 109 detects the signal travel times from the ultrasonic and infrared signal waveform inputs and transmits the signal travel times corresponding to the waveforms received at the ultrasonic receivers 102, 103 to detected value processing sections 111, 112 as time values A, B.
The time values A, B provided by the travel time difference count circuit 109 in the pen input unit 101 are converted to distance values A, B through computation by the detected value processing sections 111, 112 as shown in FIG. 23 and then to a set of coordinates values (X, Y) on the display panel 100 by the coordinate converter section 113, before the positional coordinates are displayed on the display panel 100 by the coordinate display section 114.
This ultrasonic pen input scheme requires no transparent tablet in front of the display panel 100, producing no parallax in pen input operation. Also, the scheme enables pen inputs while retaining high display quality with no transmittance degradation due to the transparent tablet.
Some pen input/display devices of the kind add new features to pen input operation. For example, Japanese published unexamined patent applications 59-220888 (Tokukaisho 59-220888/1984; published on Dec. 12, 1984) and 63-136128 (Tokukaisho 63-136128/1988; published on Jun. 8, 1988) disclose a drive method where pen pressure is sensed in a pen input operation. According to the drive method, a pen pressure sensor element provided on a pen senses pen pressure, and information on the pressure is transmitted to a display device, so that graphics are drawn on the display device in accordance with the pen pressure information.
Following are a few examples of graphics enabled by pen pressure information.
(1) Translating pen pressure information to line width information enables a brush-like feel.
(2) Translating pen pressure information to grayscale level information enables variations in grayscale level of the graphics in accordance with the pen pressure.
(3) Translating pen pressure information to color information enables changes in color of the graphics in accordance with the pen pressure. This technology is disclosed in Japanese published unexamined patent application 61-107419 (Tokukaisho 61-107419/1986; published on May 26, 1986).
In this manner, pen input operation which is simple, highly capable, and rich in features is realized using graphics information in conjunction with pen pressure information obtained by sensing.
As mentioned earlier, U.S. Pat. No. 4,814,552 scheme permits pen input while retaining parallax-free high display quality with no transmittance degradation. In addition, the drive scheme disclosed in Japanese published unexamined patent applications 59-220888 (Tokukaisho 59-220888/1984; published on Dec. 12, 1984), 63-136128 (Tokukaisho 63-136128/1988; published on Jun. 8, 1988), 63-136128 (Tokukaisho 63-136128/1988; published on Jun. 8, 1988, and 61-107419 (Tokukaisho 61-107419/1986; published on May 26, 1986) realizes a simple and highly capable, that is, rich-in-features, pen input operation whereby pen pressure is sent by a pen pressure sensor element provided on a pen and information on the pen pressure is transferred to the display device to draw graphics in accordance with pen pressure information.
The conventional pen input/display devices have large problems.
For example, in the schemes disclosed in Japanese published unexamined patent applications 59-220888 (Tokukaisho 59-220888/1984; published on Dec. 12, 1984) and 63-136128 (Tokukaisho 63-136128/1988; published on Jun. 8, 1988), information on a pen pressure sensed by pen pressure sensor means on a pen is transferred through a wireline to a display device.
In contrast, the ultrasonic pen input scheme disclosed in U.S. Pat. No. 4,814,552 works wirelessly, which is one of the scheme's attractions. Much of convenience and operability will be sacrificed if the pen is connected to the display device via a wireline to enable the transmission of pen pressure information to the display device.